I use WinRAR for all my archiving needs. When I open an archive in WinRAR, then drag its contents into a lister, Opus freezes, and cannot be used again until the extraction is complete, and the files have been moved from %temp% to their destination.
Is this normal behavior?
It is normal. I think it's just part of how drag & drop between apps usually works.
Same thing happens if you drop from WinRAR to Explorer. (Or from an archive in Opus to Explorer, for that matter.)
Dropping from Opus to Opus will do the extraction in the background, though. Extracting things via right-click or right-drag context menus also works in the background.
Thanks for the reply, leo.
I just tried using Opus for handling RAR files, and it's so fast! But I get confused opening an archive as if it were a folder. Is it possible to tell Opus to open RAR and ZIP files in a new lister? A dual pane, not full screen, with all toolbars turned off? That would be perfect 
Edit the file type in question (Settings / File types) and set the double-click event to Go NEW.